Pronounced Zonal Heterogeneity in Eocene Southern High-Latitude Sea

Supporting Information

Douglas et al. 10.1073/pnas.1321441111 SI Text Spiniferites spp., and even typical low-latitude taxa such as Apec- Further Details of the La Meseta Formation Dinocyst Biostratigraphic todinium spp. (7). Age Model. As is the case for any biostratigraphic age assignment, It is conceivable that the Weddell Sea harbored the trans- one has to assume relative synchronicity between different bio- antarctic fauna earlier than other Southern Ocean locations, and events, in this case between the East Tasman Plateau (65°S pa- excluded cosmopolitan taxa due to cooler temperatures, but there leolatitude), the Wilkes Land Margin (67°S), and Seymour Island is no independent evidence to suggest this at present. Notably, (67°S). Ocean circulation patterns derived from fully coupled there is no statistically significant correlation between the quan- ocean–atmosphere models as well as biogeographical data suggest titative distributions of endemic taxa and SST (8). The last oc- that both the southwest Pacific Tasman Sector and Seymour Is- currences of Arachnodinium antarcticum and Hystrichosphaeridium land were under the influence of Antarctic-derived ocean currents truswelliae are well documented to fall within Chron C18n (1, 2). There are no described geographic discrepancies in bio- (∼38 Ma) (3, 5). Both taxa occur in the sample from TELM 3. The stratigraphic evolution along the Cenozoic Antarctic margin, al- combined occurrence of E. diktyostyla and these taxa place the age though there are relatively few data for Antarctic biostratigraphy of TELMs 2 and 3 to between 45 and 38 Ma (Fig. S1). (3). Importantly, circumantarctic Paleogene dinocyst assemblages Enneadocysta diktyostila and a morphologically closely related constitute dinocysts that are produced by presumed autotrophic species, E. multicornuta, are abundant in samples from TELM 5. dinoflagellates (i.e., the gonyaulacoid cysts) and heterotrophic Alterbidinium distinctum is present in samples from TELM 5 and dinoflagellates (peridinioid cysts; see ref. 4 for further discussion). above. Its first consistent abundance at the East Tasman Plateau This suggests that a relatively wide array of environmental con- is at a level close to the middle-late Eocene boundary (top Chron ditions, perhaps on a seasonal scale, affected dinocyst assemblage C17n, ∼37 Ma), although spot occurrences are also reported in structure. It therefore seems unlikely that any diachronicity in older strata (3). Protoperidinioid dinocysts, mainly the heterotrophic dinocyst events arises from biogeographic isolation or differential taxa of Brigantedinium spp., Lejeunecysta spp., and Selenopemphix environmental conditions between Seymour Island and the ref- nephroides, are also present in samples from TELM 5 and above. erence sections at the East Tasman Plateau (3, 5) and on the The first abundant occurrence of these taxa at the East Tasman Wilkes Land Margin (6, 7). Plateau dates to the late middle Eocene (∼41 Ma) (12, 18), in- The dominant palynomorph groups in the La Meseta samples creasing in abundance in the late Eocene of the East Tasman are dinocysts, Paralecaniella and terrestrial palynomorphs, pri- Plateau (12, 19, 20). TELM 5 and 6 samples are devoid of A. marily Nothofagus. The preservation of the palynomorphs is good to antarcticum and H. truswelliae, potentially suggesting an age excellent, but they are quite rare in the palynological residues, younger than 38 Ma, but these taxa are rare overall and hence which are dominated by minerals insensitive to palynological sam- their absence is not necessarily diagnostic. Collectively, the di- ple processing. nocyst occurrences suggest an age older than 37 Ma for TELM 5, Samples from the Tertiary Eocene La Meseta stratigraphic but younger than 41 Ma. units (TELMs) 2–3 are characterized by abundance of typical Dinocyst assemblages in TELM 7 sediments are atypical, and these Antarctic-endemic taxa (8), notably Enneadocysta diktyostila, samples are dominated by Nothofagus pollen and Paralacaniella Vozzhennikovia apertura, Spinidinium macmurdoense, Deflandrea (Table S1). Strontium-isotope ratios from the upper part of TELM antarctica,andOctodinium askiniae. Samples from TELM 3 also 6 and TELM 7 correlate well with the global seawater 87Sr/86Sr include Arachnodinium antarcticum and Hystrichosphaeridium curve (11), suggesting that the age assignments posited by ref. 9 for truswelliae. Cosmopolitan taxa such as Operculodinium spp. and this part of the record are accurate. This means that the bulk of Spiniferites spp. are present in low abundances. Based on low overall TELM 6 is ∼41 Ma or younger, consistent with dinocyst indicators 87Sr/86Sr ratios derived from bivalve carbonate, the deposition of foranearlieragedown-section. Importantly, there is no indication TELMs 2–3 was tentatively assigned an early Eocene age (55–51 that TELM 7 sediments are as young as early Oligocene. First, there Ma) (9, 10). Variability in 87Sr/86Sr ratios, however, suggested that is no dominance of protoperidinioid taxa, which would indicate high other factors, such as freshwater mixing or incorporation of trace productivity in sea-ice–influenced conditions, commencing in the silicate minerals, could have biased the strontium-isotope data. The earliest Oligocene (6). Second, typical Southern Ocean markers uncertainty is heightened by the small degree of variance in the for the latest Eocene through earliest Oligocene interval, such as global marine strontium-isotope seawater curve for the early to Deflandrea sp. A., Stoveracysta kakanuiensis, Stoveracysta ornata, middle Eocene (11). The new dinocyst data suggest instead that the Turbiosphaera sagena, and Malvinia escutiana are not recorded in the lower part of the La Meseta Formation is no older than the base of sediments from TELM 7 (19, 21, 22). Strontium-isotope ratios for the middle Eocene, for two reasons. (i) The first occurrence of E. uppermost TELM 7 bivalve carbonates are therefore considered diktyostila (earlier assigned to Enneadocysta partridgei)(5,12) areliableindicatorthattheEocene–Oligocene boundary lies at the dominant in these samples, has been calibrated to Chron C20r top of the TELM 7 (23). (∼45 Ma) (3). (ii) E. diktyostila, Vozzhennikovia apertura, and es- sentially all other taxa present in these samples belong to the so- Standardization and Calculation of Δ47-Derived Paleotemperatures. called transantarctic fauna (13). This group of dinocyst taxa is There are no official standards for Δ47. However, several work- often referred to as Antarctic endemic, because it is biogeo- ing standards, including Carrera marble, NBS-19, cylinder CO2, graphically restricted to the circum-Antarctic Southern Ocean in and two speleothem samples, accurately characterized previously the Paleogene (8). Recent studies have shown that the onset of by numerous measurements (24, 25), were used to test for sys- dominance of these endemic dinocyst taxa around the Southern tematic errors over time and to correlate the Yale mass spec- Ocean started close to the early–middle Eocene boundary (∼49 trometer to the measurements performed in Caltech for the Ma) (8). In contrast, dinocyst assemblages spanning the early original Δ47 thermometer calibration (26). In addition, recent Eocene at the East Tasman Plateau (8, 12), the Wilkes Land interlaboratory calibration experiments (25) involving the mea- Margin (14), and New Zealand (15–17) are dominated by cos- surement of CO2 at isotopic equilibrium obtained through mopolitantaxasuchasDeflandrea oebisfeldensis, D. phosphoritica, CO2—H2O isotope exchange at several temperatures, were used

Douglas et al. www.pnas.org/cgi/content/short/1321441111 1of13 to characterize mass-spectrometric isotope effects through com- from 11.8 to 12.0 °C, an increase of 0.2 °C. Five-percent resetting parison with gas-phase theoretical values (27). This standardiza- leads to a Δ47 value of 0.694‰ (13.0 °C), and 10% resetting tion is consistent with the Yale carbonate working standards leads to a Δ47 value of 0.689‰ (14.3 °C). The shift in inferred approach and allows direct comparison of our data with published temperature under 10% resetting, 2.5 °C, is equivalent to the Δ values from other laboratories (28). 47 values are presented here typical analytical error of our Δ47 analyses (Table S3). in both the original laboratory and absolute reference frames (25). Under the extreme burial scenario (Δ47 of reset bonds = Δ Temperatures were calculated from standardized 47 values 0.232‰), 1% resetting of carbonate shifts the shell Δ47 to using the calibration of ref. 26, as revised by ref. 28: 0.695‰, equivalent to a shift from 11.8 to 12.8 °C, an increase of 1.0 °C. Five-percent resetting leads to a Δ47 value of 0.677‰ 6 10 (17.0 °C), and 10% resetting leads to a Δ47 value of 0.653‰ Δ47 = 0:0526 × + 0:0520; [S1] T2 (22.6 °C). This scenario is unrealistic, as there is no evidence that these samples were exposed to very high temperatures. Replace- 13 —18 (where T is in Kelvin) and Δ47 values are given in the original ment of either carbon or oxygen atoms in C O by solid-state reference frame used by ref. 26. This calibration was developed diffusion would lead Δ47 in the direction of a random distribution based on synthetic calcite, but has been tested using modern (Δ47 = 0.232‰ for carbonates) but at the low burial temperatures biogenic carbonates grown at known temperatures. reflected by the infilling cement and the relatively short burial External as well as internal precision should be taken into time associated with Cenozoic timescales, significant solid-state account in Δ47 measurements (28). Using the technique de- diffusion is unlikely. The results of these sensitivity tests provide scribed by ref. 28, we find that the typical external precision of a useful perspective on the maximal effects of diagenetic resetting 13 18 asingleΔ47 analysis of the Eocene bivalve fossils studied is of C— O bonds, suggesting that the potential effect on the 0.019‰, but the precision for an analysis of the modern bivalve paleotemperatures derived in this study is small. shells is 0.031‰. This difference in precision likely results from δ18 Δ δ18 a greater abundance of organic material that interferes with Δ Estimates of Ow Derived from 47 Paleotemperatures. Ow 47 Δ signals in the shells of modern bivalves. In Tables S2 and S3 we values are calculated from the 47-derived temperature and δ18 present the external error for each sample scaled by the square Ocarbonate using an empirical paleotemperature equation for root of the number of replicate analyses. Generally this value is biogenic aragonite (35), adjusted to correct for the difference be- “ ” similar to the SE of replicate Δ47 measurements for a given sample. tween average marine water andstandardmeanoceanwater(36): Â À ÁÃ Δ 18 18 Sensitivity Tests for the Effects of Diagenetic Alteration on 47 Values. T ð8CÞ = 20:6 − 4:34 × δ Oaragonite − δ Ow − 0:2 : [S2] To test for the potential effects of burial alteration on La Meseta Δ 18 Formation (Fm.) bivalve shell 47 values, we conducted a sensi- Temperature estimates from bivalve δ O measurements (Fig. 3) Δ 18 tivity analysis to predict possible shifts in bivalve shell 47 values are calculated using δ Ow estimates for individual stratigraphic 18 under both likely and extreme diagenetic alterations. We applied horizons based on a linear fit to the mean δ Ow estimates from a mass-balance mixing calculation to estimate the effects of partial horizons with Δ47 measurements (Fig. S2). We apply two distinct 13 —18 18 resetting of C O bond ordering by assuming a mixture of orig- δ Ow linear-regression models to account for a short-term shift inal and altered end members. toward more negative (<−1.5‰) values between 41.5 and 42.5 The mean δ18O and δ13C values of bivalve shell carbonate are Ma (Fig. S2). The first linear regression model is fit to all strati- ‰ − ‰ δ18 δ13 18 0.2 and 0.5 respectively, and the mean O and C graphic horizons between 34–40 and 42–45 Ma, for which δ Ow values of diagenetic void-filling cement are −3.4‰ and −4.0‰, estimates indicate a gradually increasing trend. The second linear- respectively (Table S3). The difference in stable isotope values regression model is a fit to stratigraphic horizons between 42 ∼ ‰ 18 between the shells and cement are relatively small ( 3.5 ), and and 40 Ma, an interval in which δ Ow estimates decrease in this context the effect of nonlinearity of mixing for Δ47 values sharply, likely reflecting a local deviation from the long-term trend. is negligible (29). Therefore, we compute linear mass-balance mixing between end-member Δ47 values. Seasonality of Bivalve Temperature Estimates. Evidence from high- As the unaltered end member we use a shell Δ47 value of resolution oxygen and carbon-isotope measurements of bivalve 0.700‰, at the lower end of the values we observe in La Meseta shells from the La Meseta Fm. suggests that Cucullaea shell Fm. bivalve shells (Table S3) and equivalent to 11.8 °C. We as- growth was biased toward austral winter, with growth cessation sume a likely burial temperature to be 40 °C, corresponding to during summer (9, 32). In contrast, Eurhomalea grew through a Δ47 value of 0.588‰, as implied by the Δ47 values of diage- much of the annual cycle, with slight truncation of growth during netic void-filling cement and consistent with burial to ∼1km the peak austral summer and winter (9). The difference in mean (30). As an extreme end member we assume burial carbonate values between these taxa is not evident in TELMs 6 and 7, Δ47 values of ∼0.232‰, equivalent to a stochastic distribution of suggesting more similar seasonal growth patterns during the late- 13C—18O bonds in carbonate (31). We assume that alteration of middle and late Eocene (9). Due to sample size limitations and Δ47 signatures can occur either through dissolution and repre- slow overall growth rates, it is impossible to measure clumped cipitation, or through solid-state bond reordering. isotope values from individual growth bands in these species. Δ We calculate changes in sample Δ47 values caused by 1%, 5%, However, bulk shell 47 values from Cucullaea could be partially 13 18 and 10% replacement of the original C— O bonds. We con- biased toward cold season temperatures, and Eurhomalea Δ47 sider replacement of 10% of carbonate bonds to be an upper values more closely reflect mean annual temperature. There are bound on the extent of diagenetic alteration. As noted in the four intervals where both Cucullaea and Eurhomalea were main text, there are several lines of evidence indicating only measured. For two intervals in the middle Eocene (∼43 and 44 minimal dissolution and reprecipitation of La Meseta Fm. bi- Ma), bulk Eurhomalea Δ47 paleotemperatures are slightly warmer valve shells (9, 10, 32), such that alteration of 10% of the shell than bulk Cucullaea Δ47 paleotemperatures by 2.9 ± 2.3 °C and carbonate is highly unlikely. There are only limited constraints 2.4 ± 3.6 °C, respectively (Table S2). For two intervals in the late on the rate of solid-state bond reordering of 13C—18O bonds, but Eocene, the differences in mean paleotemperatures for the two it is likely to proceed very slowly at 40 °C (33, 34). taxa are less than 1 °C (±1.8 °C), corresponding to the disap- Under a likely scenario of burial at 40 °C, 1% resetting of pearance of the seasonal difference in bulk δ18O values between carbonate shifts the shell Δ47 to 0.699‰, equivalent to a shift the two taxa in the upper part of the section as well (9). The

Douglas et al. www.pnas.org/cgi/content/short/1321441111 2of13 L apparent temperature difference in the middle Eocene may in- been higher than 15 °C. A recent study found that TEX86 pro- H dicate that temperature seasonality was more pronounced during vided a better fit than TEX86 to well-preserved carbonate SST that time—a supposition supported by high-resolution oxygen- proxy records at three mid- to high-latitude Eocene localities, isotope measurements for Cucullaea indicating a seasonal tem- despite relatively warm independent SSTs estimates above 15 °C – – L perature range of 4 8 °C in the middle Eocene relative to 1 2°C at these sites (48), suggesting that the difference between TEX86 H during the late Eocene (37). However, due to the analytical un- and TEX86 may be related to environmental differences other certainty in the clumped isotope measurements, as well as time than temperature. Recent research suggests that water depth is averaging in bulk bivalve isotopic analyses, it is difficult to verify an important factor in the application of these two calibrations, H the temperature difference between the two taxa. with TEX86 being most applicable at sites with a water depth greater than ∼1,000 m (49). L The Influence of Terrigenous Glycerol Dibiphytanyl Glycerol Tetraether There are several reasons to apply TEX86 to La Meseta Fm. Lipids on TEX86 Values. Most of our sediment samples, from both sediments. First, the independent SST estimates from bivalve laboratories (14 of 18), have branched and isoprenoid tetraether clumped isotope analyses indicate temperatures near or below (BIT) index values greater than 0.4 (Table S4), a threshold above 15 °C. Second, if the difference between the two calibrations which soil-derived glycerol dibiphytanyl glycerol tetraether (GDGT) were due to other environmental differences between high- and lipids are suspected to significantly influence TEX86-derived SST low-latitude marine environments, the subpolar paleolatitude of ∼ L estimates (i.e., by more than 2 °C) (38). However, we find no in- Seymour Island ( 67°S) also favors the application of TEX86. dication that these high BIT index values imply a large influence of Third, the shallow shelf setting of the La Meseta Fm. further terrigenous GDGTs on seawater paleotemperatures calculated us- supports the use of TEXL (49). L 86 ing TEX86 in La Meseta Fm. sediments. There is no statistically The subpolar location and relatively shallow water depth of the L L significant correlation between TEX86 values, and the BIT index in East Tasman Plateau sediments suggests that TEX86 may be our dataset (R2 = 0.143; P = 0.123), and no significant difference in more accurate there as well (48, 49). However, SSTs derived L > ð k′ Þ TEX86 temperatures between samples with high ( 0.4) and low from alkenone unsaturation ratios U37 for the late middle Eo- (≤0.4) BIT index values (based on results of a Mann–Whitney rank- cene at the East Tasman Plateau are in closer agreement with sum test; P = 0.327). We therefore conclude that TEXL derived TEXH as opposed to TEXL (Fig. S3B) (18, 50). Two factors could 86 86 ′ 86 temperatures in this study are not biased by high terrigenous GDGTs. potentially bias the Uk proxy toward relatively high SST estimates. H 37 There is, however, a significant positive correlation between TEX86 First, under oxic conditions C37:3 alkenones can be preferentially 2 = = and the BIT index (R 0.51; P 0.001). degraded relative to C37:2, leading to a diagenetic warm bias of up The impact of terrigenous GDGTs, as indicated by high BIT to 4 °C (51–54). Second, there are a number of examples of sea- k′ index values, on sedimentary TEX86 temperatures have not been sonal biases in U37 SST estimates related to the seasonality of widely studied in modern systems beyond the Congo Fan and the coccolith productivity (55–57). In a high-latitude site such as the k′ North Sea (38, 39), and is likely highly dependent on the dis- East Tasman Plateau where winter is highly light-limited U37 tribution and abundance of both branched and isoprenoidal temperature estimates may be biased toward summer temperatures. GDGT lipids within the soil of a particular catchment (40). In Multiproxy SST records from other high southern latitude sites L particular, biases in TEX86-derived temperatures from samples (New Zealand, ODP 277, ODP 511) indicate broadly similar with high BIT index values have not been examined in modern patterns to those observed at Seymour Island and the East samples, and it is possible that terrigenous organic matter input Tasman Plateau. At the mid-Waipara section of New Zealand L H has a smaller effect on TEX86 relative to TEX86. SSTs derived from Mg/Ca values of planktonic foraminifera are L H Generally, although not always, inclusion of soil-derived iso- generally more consistent with TEX86 as opposed to TEX86 (48) k′ prenoidal GDGTs leads to a warm bias in TEX86-derived tem- (Fig. S3C). At DSDP site 511, U37-derived SSTs are similar to or H peratures (38, 39). Therefore, high BIT index values are unlikely warmer than TEX86 SST estimates, similar to results from the L to explain the low TEX86-derived temperatures at Seymour Island East Tasman Plateau (45) (Fig. S3E). However, at DSDP site relative to the East Tasman Plateau, where BIT index values are 277 SST estimates from TEXL , TEXH , and Uk′ temperatures ′ 86 86 37 consistently below 0.4. Furthermore, application of the TEX86 are all relatively close, and there are no consistent offsets be- k′ paleotemperature calibration, developed specifically for settings tween them (Fig. S3D). Overall, we argue that U37 temperatures with high BIT values (38, 41, 42), to La Meseta Fm. samples results have the potential to be warm biased, as discussed above, and – L in paleotemperatures with a similar range of values (10 22 °C; that the agreement between TEX86 and inorganic temperature L – Table S4) to TEX86 paleotemperatures (5 21 °C), providing proxies at Seymour Island and New Zealand supports its appli- further confidence that terrigenous GDGTs do not strongly bias cation in the Eocene southern high latitudes. However, the L L theLaMesetaFm.TEX86 paleotemperature estimates. It is pos- choice of TEX86 is clearer at Seymour Island than at other sites H sible that terrigenous GDGT input leads to a warm bias in TEX86 with warmer inferred SSTs. SST estimates that accounts for their offset with Δ47-derived SSTs (Fig. S3A). Methylation of Branched Tetraethers/Cyclization of Branched Tetraethers Continental Temperature Estimates. The methylation of branched Choice of TEX86 Calibration. The empirical relationship between tetraethers/cyclization of branched tetraethers (MBT/CBT) proxy TEX86 values and sea surface temperature is not fully un- for continental paleotemperatures is based on the distribution of derstood, as reflected by the continued revision of TEX86–SST branched GDGT lipids derived from soil-dwelling bacteria (58, 59), calibrations (43–48). The latest global core-top calibration study and has been applied in marine sediments to estimate soil tem- H L (46) suggested two distinct calibrations, TEX86 and TEX86. peratures in adjacent terrestrial regions (7). We analyzed branched L TEX86 provides the best fit to the global core-top GDGT dis- GDGT distributions in La Meseta Fm. sediments using the meth- tribution dataset and was suggested as the preferred calibration odology of ref. 58, and estimated continental paleotemperatures H for settings with annual SST at or below 15 °C. TEX86 provides using both the original MBT/CBT temperature calibration (58) and the best fit to a subset of tropical and midlatitude sites, with the revised MBT/CBT calibration (59). L a lower root-mean-square error than TEX86, and was suggested as Application of the original MBT/CBT calibration results in the preferred calibration in settings with annual SST above 15 °C. continental temperature estimates from the La Meseta Formation However, it is unclear which calibration is most applicable to between 10 and 22 °C, which are generally in good agreement with L Δ L pre-Quaternary high-latitude locations where TEX86 is applica- both the 47 and TEX86 SST estimates (Table S4). These data are ble based on modern conditions, but SSTs in the past may have also in agreement with Eocene paleobotanical continental mean

Douglas et al. www.pnas.org/cgi/content/short/1321441111 3of13 annual air temperature (MAAT) temperature estimates from and the East Tasman Plateau, reflecting reduced temperature Seymour Island that range from 8 to 17 °C (60). heterogeneity that results from circumpolar flow. It is notewor- However, applying the revised MBT′/CBT calibration (59) to thy that this result is not consistent with proxy observations in- La Meseta Fm. sediments results in a much narrower range of dicating westward surface flow across a shallow Tasman Gateway MAAT estimates, between 21 and 23 °C (Table S4), which do during the middle and late Eocene (7). Model sensitivity analy- not agree well with either SST proxy data or paleobotanical ses indicate that deep flow through the Tasman Gateway is MAAT estimates. The reason for these discrepant MAAT esti- critical for developing circumpolar flow, and that shallow surface mates between the two calibrations are unclear, although it is flow across the Tasman Gateway, up to an effective sill depth of possible that the GDGT IIIb and IIIc compounds, which are ex- 400 m, is equivalent to UVic model simulations in which the cluded from the revised calibration, may be important in de- Tasman Gateway is closed. Although the depth of shallow Tasman termining MAAT at this high-latitude locality. Furthermore, recent Gateway flow in the middle and late Eocene is not well con- studies have suggested that branched GDGTs in coastal marine strained, high sedimentation rates suggest that the gateway was sediments can also be derived from freshwater aquatic environ- less than 400-m deep before deeper opening at ∼35.5 Ma (63). ments (61, 62) and in situ production, possibly compromising MBT/ In the UVic model, under Eocene boundary conditions, the CBT continental paleotemperature reconstructions. primary global region for deep-water formation (DWF) is in the The agreement between SST estimates and MBT-CBT MAAT southeastern Ross Sea, while intermediate water formation also estimates at Seymour Island (when applying the original cali- occurs in the northern Weddell Sea. Weddell Sea–derived in- bration) is in contrast to the southwest Pacific and the Wilkes termediate waters have some influence on the deep-water tem- Land Margin, where Eocene MBT-CBT MAAT values tend to be peratures in the Atlantic, and in the Indian Sector of the Southern around 5 °C cooler than SST estimates derived from TEXL (7). 86 Ocean. In all other ocean basins, however, deep water is domi- However, due to uncertainty in the preferred MBT/CBT temperature calibration and the provenance of branched GDGT nantly composed of warmer water derived from the Ross Sea. The role of Ross Sea DWF in promoting ocean heat transport in the lipids in coastal sediments, we are reluctant to interpret these – data further. UVic model is reflected in global air sea heat fluxes (Fig. S5). The southeastern Ross Sea is characterized by strongly negative Further Details Regarding Intermediate-Complexity Climate Model air–sea heat flux, indicating that deep sinking there is associated Results. The discussion of model results in the main text fo- with a large amount of oceanic heat transport. This highly negative cuses on simulations in which the Tasman Gateway is closed to air–sea heat flux supports the hypothesis that thermohaline-driven flow at depths greater than 400 m. Simulations where the Tasman oceanic heat transport contributed to warm SSTs in the southwest Gateway is open at depth produce a distinctly different circulation Pacific. By contrast, the Weddell Sea is characterized by a much in the Southern Ocean, with development of an eastward proto- lower flux of heat from the ocean to the atmosphere (Fig. S5), Antarctic Circumpolar Current (Fig. S4D). In this configuration, indicating that intermediate sinking there did not lead to a large the UVic model shows no SST gradient between Seymour Island amount of oceanic heat transport.

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Douglas et al. www.pnas.org/cgi/content/short/1321441111 5of13 Fig. S1. (A) The magnetostratigraphically calibrated dinocyst biostratigraphic framework for the early Paleogene of the Southern Ocean (1). Up and down arrows indicate first and last appearance respectively. (B) Chronostratigraphic interpretation for La Meseta Fm. Sediments based on dinocyst biostratigraphy and bivalve Sr-isotope signatures.

1. Bijl PK, Sluijs A, Brinkhuis H (2013) A magneto-and chemostratigraphically calibrated dinoflagellate cyst zonation of the early Palaeogene South Pacific Ocean. Earth Sci Rev 124:1–31.

Douglas et al. www.pnas.org/cgi/content/short/1321441111 6of13 18 18 Fig. S2. δ Ow values calculated from Δ47-derived temperatures and δ Ocarbonate of individual bivalve shells. Error bars primarily reflect propagated analytical 18 18 errors in Δ47 and δ Ocarbonate. The gray line depicts the latitude corrected ice-free δ Ow value (−1.21‰) (1). The solid black line indicates the long-term trend 18 18 of horizon-mean δ Ow values between 34–40 and 42–45 Ma. The dashed line indicates a trend toward more negative horizon-mean δ Ow values between 40.5 and 42 Ma. Uncertainty in the timing of the short-term negative trend is associated with it crossing a major stratigraphic discontinuity (2), and only two 18 horizons have mean δ Ow values that are significantly more negative than −1.21‰. Regression lines fitting the two indicated trends are used to estimate 18 18 δ Ow to calculate paleotemperatures from bivalve δ O measurements (Fig. 4A).

1. Zachos JC, Stott LD, Lohmann KC (1994) Evolution of early Cenozoic marine temperatures. Paleoceanography 9(2):353–387. 2. Ivany LC, et al. (2008) Eocene climate record of a high southern latitude continental shelf: Seymour Island, Antarctica. Geol Soc Am Bull 120(5-6):659–678.

Douglas et al. www.pnas.org/cgi/content/short/1321441111 7of13 Fig. S3. Multiproxy SST comparisons at sites discussed in the text. Circled TEX86 data for Seymour Island have BIT values ≤0.4. Error bars in B indicate cali- L H k′ bration errors for TEX86, TEX86, and U37, applicable to all sites. Filled markers for New Zealand are from the mid-Waipara section; unfilled markers are from the Hampden section. Planktic foraminifera Mg/Ca temperatures are from Acarinina and Morozovella assuming a seawater Mg/Ca ratio of 4 mmol/mol (1).

1. Lear CH, Rosenthal Y, Slowey N (2002) Benthic foraminiferal Mg/Ca-paleothermometry: A revised core-top calibration. Geochim Cosmochim Acta 66(19):3375–3387.

Douglas et al. www.pnas.org/cgi/content/short/1321441111 8of13 Fig. S4. SST fields for alternate model configurations: (A) Standard model with 2,400 ppm pCO2;(B) Ross Sea deep sinking suppressed with 1,600 ppm pCO2; (C) Ross Sea deep sinking suppressed with 2,400 ppm pCO2;(D) Tasman Gateway open at depth with 1,600 ppm pCO2. Proxy sites discussed in the text are shown.

Fig. S5. Air–sea heat flux in the UVic model with the Tasman Gateway closed at depth and pCO2 of 1,600 ppm. Positive values indicate heat is transferred from the atmosphere to the ocean, and negative values indicate heat is transferred from the ocean to the atmosphere. The region of deep-water formation in the southeastern Ross Sea is indicated in red.

Douglas et al. www.pnas.org/cgi/content/short/1321441111 9of13 oga tal. et Douglas www.pnas.org/cgi/content/short/1321441111

Table S1. La Meseta Fm. palynological results

Deflandrea Alterbidinium Arachnodinium Batiacasphaera Cerebrocysta Deflandrea spp. Enneadocysta Enneadocysta Eocladopyxis Hystrichosphaeridium Lejeunecysta Octodinium Operculodinium Phthanoperidinium Polysphaeridium Selenopemphix Selenopemphix Senegalinium Spinidinium Spiniferites Vozzhennikovia Indeterminable Chorate Tritonites Nothofagus Angiosperm Bisaccate Taxodium Trilete Sample Dinocysts: distinctum antarcticum spp. Brigantedinium spp. antarctica (indet and pars) diktyostila multicornuta tesselata truswelliae spp. askiniae spp. stockmansii spp. armata nephroides spp. macmurdoense spp. apertura dinocysts Acritarchs: acritarchs spp. Paralacaniella Pterospermella Sporomorphs: pollen pollen pollen pollen spores

TELM 7 0187 3 32 12 9 28 1 117 1 8 1 TELM 7 0150 1 1672 TELM 6 0109 3 1 6 6 1 3 10 1 1 1 1 96 5 6 1 72 4 14 2 TELM 5 0145 2 156 66 110 142 4 TELM 5 0193 2 1 3 105 27 2 1 1 2 1 1 2 1 11 9 2 46 8 1 10 2 TELM 3 0112 2 1 7 6 2 1 2 1 1 1 32 7 8 1 84 1 13 7 1 TELM 3 0113 1 2 6 2 1 21 90 8 1 TELM 2 014 188 11 8 89 1 23 13 2 8 0o 13 of 10 oga tal. et Douglas www.pnas.org/cgi/content/short/1321441111

Table S2. Growth temperatures and Δ47 values for modern bivalve shells Growth ‡ 13 18 Taxa Growth Growth season Δ47lab * External Δ47abs T External δ Cc δ Oc † † genera Location Mineralogy temperature season source n (‰)SEerror (‰) (°C) SE error (‰) (‰)

Mytilus Milford, CT Calcite/aragonite 16.9 April– ref. 55 3 0.681 0.005 0.018 0.742 16.0 1.2 3.8 −1.69 −2.37 September Crassostrea Milford, CT Calcite 20.7 June– ref. 54 5 0.677 0.009 0.014 0.738 17.0 2.1 2.9 −1.57 −2.65 November Laturnula Seymour Island, Calcite/aragonite/ −0.8 October– ref. 58 9 0.732 0.013 0.010 0.796 5.0 2.8 2.2 0.77 3.90 Antarctica vaterite March Mercenaria Cedar Key, FL Aragonite 22.3 November– ref. 56 6 0.664 0.010 0.013 0.724 20.0 2.5 2.7 −4.03 −1.08 June Mactra La Angelina, Aragonite 10 November– Warm six 4 0.710 0.003 0.015 0.773 9.5 1.1 3.3 0.88 1.00 Argentina April months Spisula Old Orchard Aragonite 10.6 April– ref. 57 4 0.706 0.016 0.015 0.769 10.5 4.0 3.3 0.92 −0.41 Beach, ME December Chione Ilha de Itamarca, Aragonite 27.3 Year-round Minimal 5 0.636 0.012 0.014 0.695 26.9 3.5 2.9 2.12 −1.09 Brazil seasonality Astarte Svalbard, Aragonite 2.9 June– Warm six 5 0.743 0.012 0.014 0.808 2.7 2.5 2.9 1.80 3.35 Norway December months

*Δ47lab = original laboratory reference frame. † External error indicates the typical error for this sample set, scaled by the number of replicate analyses, as defined by ref. 1. ‡ Δ47abs = absolute reference frame (2).

1. Zaarur S, Affek HP, Brandon MT (2013) A revised calibration of the clumped isotope thermometer. Earth Planet Sci Lett 382:47–57. 2. Dennis KJ, Affek HP, Passey BH, Schrag DP, Eiler JM (2011) Defining an absolute reference frame for ‘clumped’ isotope studies of CO2. Geochim Cosmochim Acta 75(22):7117–7131. 1o 13 of 11 Table S3. Isotopologue and stable isotope data from La Meseta Fm. bivalve shells

‡ 13 18 18 Estimated Δ47lab* External Δ47abs External δ Cc δ Oc δ Ow † Genera Sample ID age (Ma) n (‰)SEerror (‰) T (°C) SE error (‰) (‰) (‰)SE

Cucullaea 0153C1 37.4 1 0.699 0.018 0.019 0.761 12.0 3.7 4.2 0.280 1.007 −0.77 0.79 Cucullaea 0153C4 37.4 3 0.705 0.009 0.011 0.768 10.6 1.9 2.4 0.277 1.247 −0.86 0.47 Cucullaea 0153 mean* 37.4 4 0.702 0.007 0.010 0.765 11.3 1.4 2.1 0.278 1.130 -0.82 0.33 Cucullaea 0199C1* 37.5 5 0.690 0.007 0.009 0.751 14.1 1.7 1.9 -2.494 0.902 -0.40 0.41 Cucullaea 0170 C1-shell* 41.5 3 0.696 0.015 0.011 0.759 12.5 3.2 2.4 -0.299 -0.078 -1.71 0.76 0170C1- cement N/A 4 0.610 0.016 0.010 0.667 33.8 4.4 2.1 −2.779 −3.345 −0.12 1.09 Cucullaea 0143C1 42 3 0.696 0.017 0.011 0.758 12.7 3.7 2.4 1.190 0.444 −1.15 0.86 Cucullaea 0143C3 42 3 0.696 0.010 0.011 0.759 12.6 2.2 2.4 1.675 0.347 −1.29 0.56 Cucullaea 0143 mean* 42 6 0.696 0.009 0.008 0.758 12.6 1.9 1.7 1.433 0.395 -1.22 0.46 Cucullaea 06311C1* 44 3 0.695 0.010 0.011 0.758 12.8 2.3 2.4 -1.671 0.180 -1.41 0.59 Cucullaea 0104C1 45 3 0.660 0.008 0.011 0.720 21.0 1.9 2.4 0.714 0.012 0.32 0.43 Cucullaea 0104C3 45 3 0.684 0.013 0.011 0.746 14.3 2.2 2.4 1.671 −0.802 −2.04 0.53 Cucullaea 0104C2 45 5 0.689 0.010 0.009 0.751 15.3 2.9 1.9 1.643 0.050 −0.94 0.64 Cucullaea 0104 mean* 45 11 0.677 0.007 0.006 0.739 16.8 1.6 1.3 1.343 -0.247 -0.89 0.44 Cucullaea LMF-shell N/A 3 0.682 0.009 0.011 0.743 15.9 2.1 2.4 −1.200 −0.184 −1.16 0.58 LMF- cement N/A 3 0.577 0.011 0.011 0.632 43.4 3.4 2.4 −5.199 −3.431 1.97 0.82 Eurhomalea 0182E30 34 4 0.677 0.008 0.010 0.739 16.9 1.8 2.1 −1.075 1.019 0.26 0.40 Eurhomalea 0159E31 34 3 0.694 0.009 0.011 0.765 13.0 2.0 2.4 −0.897 1.047 −0.60 0.58 Eurhomalea 0159E30 34 2 0.712 0.015 0.013 0.775 9.2 3.1 3.0 0.222 1.060 −1.46 0.61 Eurhomalea 0182/0159 mean* 34 9 0.694 0.007 0.006 0.757 13.0 1.5 1.4 -0.583 1.042 -0.60 0.35 Eurhomalea 0153E51 37.4 3 0.698 0.004 0.011 0.760 12.2 0.8 2.4 -0.232 0.653 -1.07 0.17 Eurhomalea 0199E2 37.5 2 0.696 0.005 0.013 0.758 12.7 1.2 3.0 −2.892 1.118 −0.51 0.03 Eurhomalea 0199E5 37.5 3 0.689 0.004 0.011 0.751 14.3 0.9 2.4 −3.418 0.949 −0.31 0.22 Eurhomalea 0199 mean1 37.5 5 0.692 0.003 0.009 0.754 13.5 0.7 1.9 -3.155 1.033 -0.41 0.13 Eurhomalea 0163E1 40.5 3 0.702 0.020 0.011 0.765 11.3 4.3 2.4 −1.952 −0.734 −2.64 0.97 Eurhomalea 0163E3 40.5 1 0.687 0.011 0.019 0.749 14.6 3.2 3.2 −2.153 −2.248 −3.42 0.73 Eurhomalea 0163 mean1 40.5 4 0.695 0.015 0.010 0.757 12.9 3.2 2.1 -2.052 -1.491 -3.06 0.71 Eurhomalea 0108E2 41 3 0.692 0.010 0.011 0.754 13.6 2.2 2.4 −2.433 −0.947 −2.36 0.50 Eurhomalea 0108E5 41 3 0.704 0.009 0.011 0.767 10.9 2.1 2.4 −1.076 −0.554 −2.59 0.50 Eurhomalea 0108 mean1 41 6 0.698 0.007 0.008 0.760 12.2 1.5 1.7 -1.755 -0.751 -2.47 0.32 Eurhomalea 0143E3 42 5 0.678 0.008 0.009 0.739 16.7 1.8 1.9 1.233 −0.073 −0.75 0.39 Eurhomalea 0143E5 42 2 0.688 0.004 0.013 0.750 14.4 0.8 3.0 1.642 0.257 −0.98 0.24 Eurhomalea 0143 mean1 42 7 0.683 0.006 0.007 0.745 15.5 1.3 1.6 1.433 0.395 -0.87 0.28 Eurhomalea 0124E41 44 3 0.684 0.012 0.011 0.746 15.2 2.8 2.4 -0.682 -0.464 -1.48 0.68

*Horizon mean values are listed in bold font. Horizons with a single shell sample are also listed in bold font. † Δ47lab = original laboratory reference frame. ‡ External error indicates the typical error for this sample set, scaled by the number of replicate analyses, as defined by ref. 1. { Δ47abs = absolute reference frame (2).

Douglas et al. www.pnas.org/cgi/content/short/1321441111 12 of 13 Table S4. La Meseta Fm. GDGT lipid paleoenvironmental proxy data MAAT MAAT SST SST SST (MBT- (MBT′- H L Sample Age (TEX86 ) (TEX86 ) (TEX86′) BIT MBT MBT’ CBT CBT) CBT) L H ID (Ma) Lab TEX86 TEX86 TEX86 (ref. 1) (ref. 1) (ref. 2) (ref. 3) (ref. 4) (ref. 5) (ref. 4) (ref. 4) (ref. 5)

SI 01–80 34 Yale 0.475 −0.481 −0.323 16.5 14.5 13.6 0.427 0.485 0.818 0.661 12.0 22.4 SI 01–53 37.4 Yale 0.493 −0.537 −0.307 17.6 10.7 14.9 0.318 0.429 0.798 0.584 9.9 22.2 SI 01–99 37.5 Yale 0.434 −0.616 −0.363 13.8 5.3 10.3 0.368 0.440 0.810 0.626 10.1 22.4 SI 01–50 38 NIOZ 0.663 −0.474 −0.178 26.4 14.9 19.8 0.847 0.750 0.886 1.039 21.7 22.4 SI 01–54 38.4 NIOZ 0.499 −0.510 −0.302 17.9 12.5 14.7 0.373 0.519 0.783 0.593 14.3 21.7 SI 01–09 39.5 NIOZ 0.531 −0.502 −0.275 19.8 13.0 14.8 0.640 0.582 0.858 0.873 14.8 22.5 SI 01–66 40.5 Yale 0.486 −0.574 −0.313 17.2 8.1 11.5 0.508 0.605 0.808 0.679 17.8 22.0 SI 01–08 41 Yale 0.486 −0.575 −0.314 17.2 8.1 11.6 0.621 0.516 0.856 0.826 12.0 22.7 SI 01–69 41.6 NIOZ 0.570 −0.486 −0.244 21.9 14.1 17.0 0.688 0.630 0.884 0.996 16.1 22.6 SI 01–46 41.8 NIOZ 0.602 −0.433 −0.221 23.5 17.7 19.3 0.738 0.600 0.881 0.969 14.8 22.6 SI 01–45 41.9 Yale 0.531 −0.541 −0.275 19.8 10.4 13.5 0.670 0.584 0.885 0.948 14.2 22.9 SI 01–93 42 NIOZ 0.612 −0.383 −0.213 24.0 21.0 22.1 0.637 0.613 0.892 1.005 15.1 22.7 SI 01–44 42 Yale 0.563 −0.491 −0.250 21.5 13.7 15.1 0.674 0.564 0.875 0.917 13.5 22.7 SI 01–40 43.5 NIOZ 0.582 −0.435 −0.235 22.5 17.5 19.9 0.407 0.590 0.785 0.599 17.8 21.7 SI 01–16 43.8 Yale 0.567 −0.450 −0.247 21.7 16.5 16.9 0.734 0.627 0.931 1.320 12.9 22.2 SI 01–12 44 NIOZ 0.543 −0.489 −0.266 20.4 13.9 16.6 0.469 0.625 0.875 0.932 16.4 22.7 SI 01–21 44 Yale 0.547 −0.438 −0.262 20.7 17.3 17.3 0.624 0.646 0.827 0.888 17.9 21.4 SI 01–04 45 Yale 0.555 −0.501 −0.256 21.1 13.1 15.0 0.646 0.574 0.882 0.941 13.8 22.8

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Douglas et al. www.pnas.org/cgi/content/short/1321441111 13 of 13